Measuring Brain Activity

Psy391D - Class 19

Methods for Studying the Brain

• Single Cell Recording
  • Electrode through skull and into brain.
  • Records differences in electrical potential over time in a single neuron or small group of neurons.
  • Action potentials
    • All-or-none firing
    • Firing rate varies depending on strength of input.
  • Excellent temporal and spatial resolution
• Electroencephalogram (EEG)
  • Electrodes placed on scalp.
  • Each electrode measures changes in electrical potential at its location.
  • Measurement from each electrode reflects activity from large numbers of neurons.
  • Neurons near brain surface produce stronger signals than those deep in the brain.
  • Signals can be combined to produce maps of activation across brain surface.
  • Temporal resolution excellent. Spatial resolution not as good.
• X-Ray Computed Tomography (CT or CAT)
  • Multiple X-ray images
  • Combined computationally
  • Produces images of slices through brain (or other parts of body).
  • Very useful for localizing damage.
  • Shows only structure, not function.
• Positron Emission Tomography (PET)
  • Radioactive substance introduced to bloodstream
    • Injected
    • Inhaled
  • Ring of detectors around head record positrons from radioactive decay
  • Active areas of brain receive more blood, and thus produce more positrons.
  • Can computationally produce images of brain slices.
  • Different colors show different levels of blood flow and thus different levels of brain activity.
  • Shows function, but not structure.
  • OK spatial resolution. Poor temporal resolution.
• Nuclear Magnetic Resonance Imaging (MRI)
  • Giant magnet creates strong magnetic field.
  • Molecules align to magnetic field.
  • Sudden radio pulse knocks them out of alignment.
  • Different types of molecules produce different responses.
  • Can produce maps showing concentrations of different substances
  • Shows structure, not function.
• Functional Magnetic Resonance Imaging (fMRI)
  • Use MRI to measure blood flow (and therefore activity) in brain.
  • Shows brain function.
  • Colors representing different levels of activity can be added to structural images of brain slices or brain surface.
  • Both spatial and temporal resolution improving.
• Transcranial Magnetic Stimulation (TMS)
  • Produces brief magnetic pulse.
  • Can interfere with brain activity within small region near surface.
  • TMS in motor areas can produce sudden movement.

     

Psych 391D: Consciousness Kyle Cave Psychology Dept. U. Mass.